Communication:Displays

Definition Of A Display

• A display is an output device that communicates with a human.

Interfaces• The displays providing feedback to the

human about the status of the machine of the behavior of the whole system.

• The controls by which the operator inputs feed forward affecting the system.

Matching the Display with Information Requirement

• It is important that the instrument gives the operator only the information required, for instance by displaying the smallest unit that the operator is likely to read off.

Matching the Display with Information Requirement

• Sometimes the operator does not need a precise reading but just to know a range. Here a moving pointer is best and the various ranges should be marked by different color.

Dynamic Displays

• Quantitative– Exact Information

• Qualitative– General Condition or

Status

Check-reading Displays

• Check-reading displays are a specific type of qualitative display in which you determine whether the value of a continuously changing variable is normal, or within an acceptably normal range.

Qualitative vs Quantitative Displays

1. Fixed scale & moving pointer − speedometer

2. Fixed pointer & moving scale− analog bathroom scales

3. Digital display− digital watch

Digital vs. Analog Displays

• Digital Displays – Preferred when precise

numeric values are required, legible digits are needed quickly or the value remains stable for a long enough period to be read

Types of DisplaysType of Display Moving Pointer Fixed Marker

Moving ScaleDigital Counter

Ease of Reading

Acceptable Acceptable Very Good

Detection of Change

Very Good Acceptable Poor

Setting to a Reading or Controlling a Process

Very Good Acceptable Acceptable

Design of Scale Graduations

1. The height, thickness and distance of scale graduations must be such that they can be read off with minimal likelihood of error, even if lighting conditions are not ideal.

Design of Scale Graduations

2. The information presented should be what is actually wanted: scale divisions should not be smaller than the accuracy required; qualitative information should be simple and unmistakable.

Design of Scale Graduations

3. Scale graduations should give information that is easy to interpret and to make use of. It is laborious to have to multiply the reading of the instrument by a factor. If this is unavoidable, then the factor should be as simple as possible.

4. Subdivisions should be by ½ or 1/5: anything else is difficult to read off.

Design of Scale Graduations

5. Numbers should be confined to major scale graduations and, once again, subdivisions should be ½ or1/5.

6. The tip of the pointer should not obscure either the numbers of the graduations and if possible should not be broader than a scale line. It is best if the tip of the pointer comes as close as possible to the scale, without actually touching it.

Design of Scale Graduations

7. The pointer should be as nearly as possible in the same plane as the graduated scale, to avoid errors of parallax, and the eye must be positioned so that the line of sight is at right angles to the dial and pointer.

Scale Graduations

Height of biggest graduations a/90Height of middle graduations a/125Height of smallest graduations a/200Thickness of graduations a/5000Distance between two small graduations a/600Distance between two big graduations a/50

Background and Lettering• Black letters on a white background are

preferred, in principle, because white characters tend to blur, and a black background may set up relative glare against its lighter surroundings.

Text SizeBreadth 2/3 of heightThickness of line 1/6 heightDistance apart of letters 1/5 of heightDistance between words and figures 2/3 of height

Viewing Angle

• The preferred angle of view for displays (the angle at which the display plane is positioned with regard to the person monitoring it) should be 90 degrees.

Analog Display Design

• Moving pointer on a fixed scale is preferred.

• If numerical change relates to natural function (e.g. up/down) then vertical display is preferred to circular display.

• Types of pointer-scales should not be mixed to indicate related functions in displays.

• Direction of movement of pointer should match that of the control.

Analog Display Design• If value must be read quickly then

a moving scale appearing in an open-window is best..

• Semi-circular or circular displays preferable to horizontal or vertical displays.

• Adjacent scales should have similar markings and be oriented to the same point to indicate normal operation. This is exemplified with check scales

Analog Displays: Scale Markings

• Marker length depends on level of illumination - markers must be thicker and farther apart in low light.

• Markings should be presented for the smallest scale unit that needs to be read.

• Use different interval markers (in gradations like a ruler).

• Zero should be placed at 6 o'clock or 12 o'clock (standard for auto industry is 7 o'clock however)

Analog Displays: Numerical Progression

• Intervals of 1 are easiest to read (0, 1, 2, ...)

• Decimal progression is the second most preferred (10, 20, 30,...)

• Units of 5 is the next best (5, 10, 15, ...) intervals of 2 are also OK(2, 4, 6, ...)

• Avoid unusual progressions (e.g. by 3, by 7, by 8)

• Scale intervals should represent consistent progressions (all intervals should equal the same amount)

Control and Display Rules

• Controls and instruments which are functionally linked should make corresponding movements that comply with our own stereotypes.

Control and Display Rules

1. When a control is moved or turned to the right, the pointer must also move right over a round or horizontal scale; on a vertical scale the pointer must move upwards.

2. When a control is moved upwards or forwards, the pointer must move either upward or to the right.

Control and Display Rules3. A right-handed or clockwise rotation

instinctively suggest an increase, so the display instrument should also record an increase.

Control and Display Rules4. A moving scale with a fixed pointer

indicator should move to the right when the control is moved to the right but the scale values should increase from right to left, so that a rotation of scale to right gives increased readings.

Control and Display Rules5. When a hand lever is moved upward, or

forward, or to the right, the display reading should increase or the equipment should be turned on. To reduce the reading, or to switch off, it is instinctive to pull the lever toward the body or move it to the left, or downward.

Conclusion• Good Visibility

– See it• Good Comprehension

– Make correct decisions• Good Compatibility

– Easily used with others